In general, an adjustable spanner must be used to screw various kinds of screwing element. As a result, the adjustable spanner is easy to be destroyed. Thus, it is very necessary that the adjustable spanner has a stronger strength for suffering from stronger twisting force. In one prior art, the spanner body of the adjustable spanner has a sliding track for receiving a movable jaw. The track has a reverse Ω slot. However the sliding track is in contact with the movable jaw in a small area so that the structure strength is low. Moreover, in some prior art, an enhancing structure is installed at an upper side of the movable jaw, but most of the stress is concentrated in the neck portion of the movable jaw so that the effect of enhancing the structure is low, and thus the movable jaw be destroyed as it is used for a longer time.